Half Life 2
Storyline Half Life 2 is the direct sequel to the critically acclaimed Half Life (1998) where the player assumes the identity of a gun-wielding scientist named Gordan Freeman where he must free the enslaved population of Earth by another distant dominant alien race known as the Combine. In the first game, Gordan Freeman, during an experiment in the underground lab known as Black Mesa makes a critical mistake unleashing a portal to a strange alien world known as Xen in the lab. Strange, hostile aliens are able to appear at their own will. They quickly slay most of the scientists and unprepared security guards as a consequence. The government is also attempting to cover this catastrophic event by sending in Black ops to silence every potential witness including the scientists and security guards. Gordan Freeman fights his way through the military and the aliens until finally he finally defeats the Nihilanth in the Xen world and closing the portal. However he is held in a stasis like event by an unknown human figure named "G-Man" where Gordan is offered a contract and accepts it. It is unclear what the "G-Man's" final goal is and whether he actually cares for the fate of the Earth. After being held in stasis an unknown civilization consisting of humanoid aliens invade Earth taking advantage of the recent events that occured and conquer Earth in just 7 hours. Their superior soldiers and technology gave the name of the war "The 7 Hour War". Consequently most of the population was obliterated and the survivors were sent as slaves to work for the Combine to extract resources for them. Some were taken away to undergo horrible experimentation where important organs such as the lungs were removed and machinery and chips were replaced and became servants for the Combine and they were unrecognizable as human beings. These people became the police force imposing strict laws and instilling fear into the slaves. The ones which escaped from the Combine formed their own rebellion group which was sprawled all over the city however they are quite powerless without Gordan Freeman. Quite soon though the "G-Man" decides to take action and wake Gordan Freeman from his stasis explaning that his time has come again and that the right man in the wrong place can make all the difference. This is where the events of Half Life 2 start where he is awaken by "G-Man" and is on a train on the way to City 17. Gordan is surrounded by human workers and passes the Combine checkpoints unnoticed. However he is soon called up during a line inspection and is leaded into an interrogation room with one of the Combine police member. To his surprise however, it turns out to be one of his co-workers back from Black Mesa (Half Life) Barney and explains to Gordan that he is infiltrating the Combine to give information for the rebels. He leads Gordan away from the Combine checkpoints to make his escape into an underground rebel base which has a laboratory. Along the way however the Combine are alerted to his presence and pursue him and almost catching him until a girl named Alyx saves his life. She escorts Gordan to the underground base and there he meets another colleague named Dr. Kleiner. Gordan was briefed on how he must go to the teleporter in their base to aid a large rebel base to begin their assault on the Combine. However a mistake happens and when Gordan steps into the teleporter he is transported into the middle of Combine territory and is forced to fight his way through. After reaching the rebel base he meets up with Alyx again and her father, Eli Vance. However, the Combine are now fully alert to Gordon's presence and have knowledge of his whereabouts. They quickly mount up a counter-attack before the rebels can prepare for their own and the base is destroyed and abandoned. The Combine have captured Eli Vance and are holding him in the prison center known as Nova Prospekt. Alyx quickly explains to Gordan that she is heading there to save her father before departuring Separated once again from his comrades, Gordan escapes to a nearby mining town called Ravenholm which is seemingly abandoned. However he soon encounters mutated humans with a parasatic creature sitting on their heads known as headcrabs. These creatures latch on to an unfortunate victim's head with their sharp teeth and mutation begins to occur ripping their chest open and exposing their rib cage but technically they are not considered to be dead yet and undergo unbearable pain until someone kills them or the parasite. Different variations of these zombies occur depending on the type of headcrab. After Gordan escapes clears his way through the mining town with one surviving priest he soon leaves him and heads back out in the middle of a skirmish between the rebels and the Combine. Gordan once again defeats the Combine and the rebels give him aid by giving Gordan his own car. He soon travels across the desert encountering more aliens known as antlions along the way which are giant insect-like creatures. He manages to kill the broodmother of the Antlions and takes the heart which is still beating. With it he is able to control other Antlions to attack other foes or follow him. Gordan is now near Nova Prospekt which is a heavily guarded prison but with his army of Antlions now under his command he quickly eradicates the base and rescues Eli Vance and meets Alyx Vance as well and together they escape Nova Prospekt. Little did they know that one of their own was working for the Combine acting as a spy and they are soon betrayed with Eli Vance being captured once again but this time in the Combine Headquarters which is a giant citadel guarded by the Combine Elite. Gordan and Alyx attempt to chase the traitor down by going in the near-by teleporter. However another miscalculation happens and they are transported back into the rebel lab base but this time two weeks ahead! With the rebels thinking that they have lost Gordan their leader and Alyx Vance they soon begin an all out rebellion causing chaos and total security alert by the Combine. With Alyx and Gordan joining them the tides soon turn and the Combine are pulled into a retreat back into the Citadel where the pair are on the pursuit. Unfortunately Alyx is soon captured by the Combine and is placed in the Citadel along with her father and Gordan is forced to rescue both of them. The ambassador of the Combine, a human named Breen who was bought out by the Combine has a plan to lure Gordan in and capture him. After fighting through a horde inside the Citadel with the upgraded gravity gun he is soon forced to take the only path to rescue Alyx and Eli, through the hands of the ambassador. Gordan is now captured and Breen has all three of the important leaders of the rebellion. He attempts to persuade Eli to call off the rebellion but he stubbornly refuses. Just as Breen was about to go to drastic measures by using Gordan's gravity gun against him he misfires it and creates an explosion buying them a distraction and enough time to release themselves from their captors. Breen who was in immediate danger flees the scene and puts the Citadel in an automatic self destruct sequence while he attempts to escape with the Combine Elite Guard holding back Gordan and Alyx. However he is unsuccessful and Gordan malfunctions the teleporter in the Citadel causing huge explosion and killing Breen. The "G-Man" comes in the scene and stops time saving Alyx and Gordan from the blast and putting Gordan into another stasis. The "G-Man" congratulates Gordan for the damage he has done to the Combine in such a short amount of time and assures him that when and if Gordan's time comes around again he will be awoken and everything will come to sense. However the player is shrouded into darkness even more confused and wondering what the "G-Man's" next plan is. = Half Life 2 engine (Source engine) The source engine was developed by Valve and is most known for powering some of the most popular fps shooters such as Counter Strike and Half Life 2. Originally developed off the old goldsrc engine back in 1998 it was re-written to include improvements which would meet the audience’s demand for more realistic interactions between the players, the environment and the AI computer in games. Some of the notable effects of the source engine include real-time physics interaction and collision detection by objects and players, a user friendly facial animation used to create cut scenes and cinematic moments, soft particle simulation where grass and trees were rendered more smoothly and advanced high dynamic range used to imitate realistic lighting scenes by calculating the required amount of glow and particles on a larger scale. The AI in the Source Engine is unscripted and the interaction between the objects /enemies/companions is dynamic and continuous. This results in the player being able to join in fire fights at their own will or flee to a safe place. The player is even able to do both in varying degrees and also able to use the environment to their advantage such as blowing up oil barrel drums to ignite the enemy or fling sharp building debris into the enemy with the appropriate gadgets. The battle AI also works as a team or a squad to hunt the player sharing information, reporting their status and covering each other. A fine example of this is while one squad member supresses the player while another may find the opportunity to rush and flank the player. The dynamic AI behaves differently for every new game started which requires the player to have a different strategy or adapt to a new situation. This is shown in the demonstration video where two different forces of AI have a skirmish with one force fortifying a building and the other attempting to assault it. Half Life 2 uses the very base core of the Havok engine to reproduce its physics. This supports more advanced features such as inverse kinematics and forward kinematics for more real movements in the AI and other objects. Kinematics is the required mechanical movements to achieve a desired objective. An example of this is running to a particular spot to grab an object. The developer must calculate the position and the angles of each part of the legs and arms to create a believable figure running. In addition the developer must also calculate the angles and position of the other bones in the figure such as the fore arm and arm. Not only can the engine simulate movements of people but it can also calculate the destruction of buildings and objects. By having a scripted sequence the developer is able to input data such as explosion magnitude and direction and what type of material to explode such as stone or wood etc. The Source engine now also supports ‘cinematic physics’ which enables the developer to pre-animate a model to break into pieces after an explosion in an external application to put back into the game enabling even more realistic destruction of buildings or the environment. The physics of the game is present in the demonstration video where the destruction of a temple takes place. [[Video:Half Life 2 Game Engine|thumb|left|300px|Video Showing the ai intertaction and Physics of Half Life 2.]]